Methods and systems for solid state heat transfer

ABSTRACT

Various embodiments are directed to a thermoelectric device comprising a thermoelectric element, a first heat switch and a second heat switch. The thermoelectric element may comprise a first component in electrical contact with a second component at an interface. The first component may comprise a first material and the second component may comprise a second material different from the first material. The first heat switch may comprise a first terminal in thermal contact with the interface and a second terminal in thermal contact with a thermal reservoir. The second heat switch may comprise a first terminal in thermal contact with the interface and a second terminal in thermal contact with a thermal load.

This application is a continuation of U.S. patent application Ser. No.13/050,555, entitled METHODS AND SYSTEMS FOR SOLID STATE HEAT TRANSFER,filed on Mar. 17, 2011 and is incorporated herein by reference in itsentirety.

BACKGROUND

Many known thermoelectric devices utilize the Peltier effect for heatingor cooling. Typically, a direct current is provided across asemiconductor material and/or across an array of interconnectedsemiconductor materials of different types (e.g., semiconductormaterials having different doping properties). As a result of thecurrent, the junction either generates heat or rejects heat (cooling).The heating or cooling effect of thermoelectric devices is used in anumber of contexts ranging from superconductivity to microprocessorcooling devices to electric beverage coolers.

The Figure of Merit (FOM) describing the performance of typicalthermoelectric devices is given by Equation (1) below:Z=S _(e) ² k _(e) /k _(T)  (1)In Equation (1), Z is the FOM; S_(e) is the Seebeck coefficient of thedevice; k_(e) is the electrical conductivity of the device and k_(T) isthe thermal conductivity. It can be seen that the performance ofthermoelectric devices (Z) is proportional to electrical conductivityand inversely proportional to thermal conductivity. In other words, highelectrical conductivity of the device material improves performance,while high thermal conductivity of the device material degradesperformance. Accordingly, the ideal material for thermoelectric deviceswould be one that has a high electrical conductivity and a low thermalconductivity. Unfortunately, for most practical materials, electricaland thermal conductivity are proportional. As a result, existingthermoelectric devices suffer performance degradation due either to anexcess of thermal conductivity or a lack of electrical conductivity.

FIGURES

Various embodiments of the present invention are described here by wayof example in conjunction with the following figures, wherein:

FIG. 1 illustrates a diagram showing one embodiment of a thermoelectricelement.

FIG. 2 illustrates a diagram showing one embodiment of an alternateconfiguration of the thermoelectric element of FIG. 1.

FIGS. 3(a)-3(d) illustrate a process flow showing the operation of oneembodiment of the thermoelectric element of FIG. 1 or 2.

FIG. 4 is a chart illustrating a temperature-entropy (TS) cycle of thethermoelectric element, during implementation of the process flow ofFIGS. 3(a)-3(d).

FIGS. 5(a)-5(d) illustrates a process flow showing the operation of oneembodiment of a plurality of thermoelectric elements operating inparallel.

FIGS. 6(a)-6(b) illustrate a process flow showing the operation of oneembodiment of a compound thermoelectric element.

FIG. 7 illustrates a diagram of one embodiment of a heat switch.

FIG. 8 illustrates a diagram of another embodiment of a heat switch.

DESCRIPTION

Various embodiments are directed to thermoelectric devices fortransmitting heat energy from one thermodynamic body to anotherutilizing heat switches and current provided in varying directions. Thedevices described herein may be used to cool a body (e.g., a waste-heatgenerating device such as a piece of electronic or mechanical equipment,a device to be cooled for operation such as a cooler, refrigerator orsuperconductive material, etc.). The devices described herein may alsobe used, in some embodiments, to heat bodies.

According to various embodiments, the devices described herein maycomprise one or more thermoelectric elements thermally positionedbetween a thermal reservoir (e.g., to be heated) and a thermal load(e.g., to be cooled). Each thermoelectric element may comprise a firstcomponent made from a first material and a second component made from asecond material. The first component and the second component may be inelectrical contact with one another via an interface which may, forexample, comprise an electrically conductive material, such as a metal.The first and second materials may have different Seebeck coefficientssuch that current across the interface in one direction tends togenerate heat at the interface and, in some embodiments, draw heat tothe interface while current across the interface in the oppositedirection tends to push heat away from the interface, resulting incooling. For example, in various embodiments the first material may bep-type semiconductor material and the second material may be n-typesemiconductor material. The interface may be alternately thermallycoupled and thermally insulated from the thermal reservoir and thermalload via one or more heat switches. For example, a heat switch may havea first terminal and a second terminal. When the temperaturedifferential across the first and second terminals exceeds a heatswitching threshold, the heat switch may close, creating a thermallyconductive path between the first and second terminals. Similarly, whenthe temperature differential across the first and second terminals dropsbelow the heat switching threshold, the heat switch may open, thermallyinsulating the first and second terminals.

In use, a control circuit may cause electric current to flow, across theinterface in a first direction, causing the interface to heat. This mayraise the temperature differential between the interface and the thermalreservoir, causing the first heat switch to close, thereby allowing heatfrom the interface to be dissipated to the thermal reservoir (e.g.,ambient air or other material). When enough heat is dissipated to reducethe differential between the interface and the thermal reservoir, thefirst heat switch may re-open. The control circuit may alternately causeelectric current to flow across the interface in a second direction,opposite the first, causing the interface to cool. Cooling the interfacemay increase the temperature differential between the interface and thethermal load and may, in some embodiments, generate heat on its own.This may, in turn, cause the second heat switch to close, allowing heatfrom the thermal load to be transferred to the interface until thetemperature differential between the interface and the thermal loaddrops below a threshold for the second heat switch, at which point thesecond heat switch may close, thermally isolating the interface from thethermal load. In this way, the thermoelectric element may operate as aheat pump to pump heat away from the thermal load and towards thethermal reservoir. Also, in some embodiments, the operation of the heatswitches may serve to prevent undesirable heat conduction in thethermoelectric element, mitigating efficiency losses due to thermalconductivity.

FIG. 1 illustrates a diagram showing one embodiment of a thermoelectricdevice 100. The device 101 may comprise a thermoelectric element 100.The thermoelectric element 100 may comprise a first component 102 and asecond component 104 in electrical contact with one another at aninterface 106. The first and second components 102, 104 may be made fromand/or may contain materials having different Seebeck coefficients suchthat current across the first and second components 102, 104 in a firstdirection causes cooling at the interface 106 and current across thefirst and second components 102, 104 in a second direction causesheating at the interface 106. For example, in various embodiments, thefirst component 102 may be made from and/or contain p-type semiconductorwhile the second component 104 may be made from and/or contain n-typesemiconductor. In embodiments where the components 102, 104 are madefrom different kinds of semiconductors, the element 100 may beconfigured such that the p-type and n-type materials do not create arectifying pn junction. For example, it may be possible to pass currentfrom p-to-n as well as from n-to-p. This may be achieved in any suitablemanner. For example, the interface 106 may be made from and/or include ametal or other conductive material that may form an ohmic connectionwith one or both of the components 102, 104. In various embodiments, theinterface 106 may electrically separate the components 102, 104 by adistance exceeding the thickness of a hypothetical depletion region thatwould result from joining the first and second components 102, 104.

The thermoelectric device 101 may also comprise first and second heatswitches 108, 110 alternately creating and blocking thermal connectionsbetween the interface 106 and an ambient thermal reservoir 112 on theone hand, and a thermal load 114 on the other hand. The heat switch 108may have a first terminal 116 in thermal contact with the interface 106and a second terminal 118 in thermal contact with the thermal reservoiror ambient 112. The thermal reservoir or ambient 112 may be a thermalmass that may receive heat from the element 100. For example, thethermal reservoir or ambient 112 may be the ambient air or othermaterial surrounding the element 100. The heat switch 110 may have afirst terminal 120 in thermal contact with the interface 106 and asecond terminal 120 in thermal contact with a thermal load 114. Thethermal load 114, for example, may be an object to be cooled such as asensor, microprocessor, etc. Each of the heat switches 108, 110 may havean open state, where the respective heat switch terminals 116, 118, 120,122 are thermally isolated from one another and a closed state where therespective terminals are in thermal contact with one another. The heatswitches 108, 110 may be actuated in any suitable manner. For example,in some embodiments, the heat switches may be actuated between closedand open states by a control circuit 130, as described below. Further,in some embodiments, the heat switches 108, 110 may be thermal switchesthat are actuated between closed and open states, for example, based ona temperature differential across the respective heat switches 108, 110.For example, when the temperature differential exceeds a closingthreshold, a thermal switch may close. When the temperature differentialdrops below an opening threshold, the thermal switch may open. Accordingto various embodiments, one-way thermal switches may be used. One-waythermal switches may open or close only in response to temperaturedifferentials in one direction. For example, switch 108 may be a one-wayswitch that closes in response to the interface 106 becoming warmerrelative to the ambient 112 and opens in response to the interface 106becoming cooler relative to the ambient 112.

A control circuit 130 may control operation of the device 101. Forexample, the control circuit 130 may control the presence or absence, aswell as the direction, of current passed through the components 102, 104and interface 106 of the element. For example, the control circuit 130may comprise and/or be in communication with one or more power suppliesfor generating current. Further, in some embodiments, the controlcircuit 130 may control actuation of the heat switches 108, 110, asdescribed herein. According to various embodiments, the control circuit130 may be in communication with various sensors for sensing the stateof device 101 parts. For example, temperature sensors 132, 134, 136 maybe in communication with the control circuit 130 to provide temperatureinformation describing temperatures of the interface 106, the ambient112 and the thermal load 114, respectively. Also, in some embodiments,the control circuit 130 may be in communication with sensors 138, 140for sensing the position of the heat switches 110, 108, respectively.The control circuit 130 itself may be any suitable form of controldevice including, for example, an analog circuit, a digital circuit, amixed analog and digital circuit, etc. In some embodiments, the controlcircuit 130 may comprise a microprocessor.

FIG. 2 illustrates a diagram showing one embodiment of an alternateconfiguration of the thermoelectric device 101. The device 101, as shownin FIG. 2, demonstrates that many different spatial configurations arepossible. For example, in FIG. 2, the interface 106 is illustratedconnecting non-adjacent sides of the components 102, 104. It will beappreciated that any suitable configuration may be used.

FIGS. 3 and 4 illustrate the operation of one embodiment of thethermoelectric device 101. FIG. 3(a)-3(d) illustrate a process flowshowing the operation of one embodiment of the thermoelectric device101. FIG. 4 is a chart 400 illustrating a temperature-entropy (TS) cycleof the thermoelectric device 101 during implementation of the processflow of FIGS. 3(a)-3(d). In FIG. 4, temperature, or T is indicated onthe vertical y-axis, while entropy or S is indicated on the horizontalx-axis.

Referring now to FIG. 3(a), the control circuit 130 may cause a current(indicated by arrow 302) to flow across the interface 106 from thecomponent 102 to the component 104 (e.g., from p-type material to n-typematerial). Both of the heat switches 108 and 110 may be open, preventingheat transfer between the interface 106 and either the ambient 112 orthe thermal load 114. The current 302 from p-type to n-type may causethe interface 106 to heat. The TS characteristics of the thermoelectricelement 100 in the configuration shown in FIG. 3(a) are illustrated bycurve 402 of the TS chart 400. As illustrated, the entropy of theelement 100 may decrease slightly, while the temperature increases asthe interface 106 heats.

As the interface 106 heats, a temperature differential between theinterface 106 and the ambient 112 may increase. When the temperaturedifferential exceeds a closing threshold of the heat switch 108, theheat switch 108 may close, creating a thermally conductive path betweenthe interface 106 and the ambient 112. At or about the closing of theheat switch 108, the control circuit 130 may cause the current 302 tocease. This configuration is illustrated in FIG. 3(b). With the heatswitch 108 closed and the current 302 turned off, heat from theinterface 106 may be released to the ambient. This process isillustrated in FIG. 4 by curve 404. As shown, the temperature of theelement 100 may stay roughly constant, while the entropy of the elementdecreases as heat is lost to the ambient 112. In embodiments where theheat switch 108 is controlled by the control circuit 130, the controlcircuit 130 may close the heat switch based a signal received from oneor more sensors 132, 134 indicating the temperature differential betweenthe interface 106 and the ambient 112 or upon the occurrence of anyother suitable condition (e.g., the passage of a predetermined time fromthe initiation of the current 302, the passage of a predetermined levelof charge through the components 102, 104 and interface 106 from thecurrent 302, etc.).

As heat is released to the ambient 112, the temperature differentialbetween the ambient 112 and the interface 106 may decline. When thetemperature differential between the ambient 112 and the interface 106declines below an opening threshold of the heat switch 108, the heatswitch 108 may open, causing substantial thermal isolation between theinterface and the ambient 112. In embodiments where the heat switch 108is controlled by the control circuit 130, the control circuit 130 mayopen the switch 108, for example, based on a determination of thetemperature differential between the ambient 112 and the interface 106received from the sensors 132, 134 and/or any other suitable criteria(e.g., the passage of a predetermined amount of time from the closing ofthe switch 108).

At or about the opening of the heat switch 108, the control circuit 130may cause a current, indicated by arrow 304, to flow across theinterface 106 from the component 104 to the component 102 (e.g., fromn-type to p-type). The current 304 may cause cooling at the interface106. For example, the current 304 may drive heat away from the interface106. The configuration of the element 100 with the heat switch 108 openand the current 304 flowing from n-type to p-type is shown in FIG. 3(c).The TS properties of the element 100, as illustrated in FIG. 3(c) areshown by curve 406 of the chart 400. As illustrated, the temperature ofthe element 100 may decline, while the entropy increases.

As the temperature of the interface 106 declines, the temperaturedifferential between the interface 106 and the thermal load 114 mayincrease. When this temperature differential exceeds a closing thresholdof the heat switch 110, the heat switch 110 may close, creating athermally conductive path between the interface 106 and the thermal load114. In embodiments where the heat switch 110 is actuated by the controlcircuit 130, the control circuit 130 may determine when to close theheat switch 110 based, for example, on temperature readings receivedfrom sensors 132 and 136 indicating the temperature differential betweenthe interface 106 and the thermal load 114 and/or any other suitablecriteria (e.g., the passage of a predetermined time from the initiationof the current 302, the passage of a predetermined level of chargethrough the components 102, 104 and interface 106 from the current 304,etc.).

At or about the time that the heat switch 110 closes, the controlcircuit 130 may cause the current 304 to cease, resulting in theconfiguration of the element 100 shown in FIG. 3(d). Thermal energygenerated by the thermal load 114 may propagate from the relatively hotthermal load 114 to the relatively cold interface 106. The TC propertiesof the element 100, as illustrated in FIG. 3(d), are shown by the curve408. As illustrated, the temperature of the element 100 may remain aboutconstant, while the entropy of the element 100 may increase.

As heat energy from the thermal load 114 is transferred to the interface106, the temperature differential between the thermal load 114 and theinterface 106 may decline until it reaches an opening threshold of theheat switch 110. At this point, the heat switch 110 may open causingsubstantial thermal isolation between the thermal load 114 and theinterface 106. At or about the opening of the heat switch 110, thecontrol circuit 130 may cause the current 302 to flow, as illustrated inFIG. 3(a). In embodiments where the heat switch 110 is controlled by thecontrol circuit 130, the control circuit 130 may open the switch 110,for example, based on a determination of the temperature differentialbetween the thermal load 114 and the interface 106 received from thesensors 132, 134 and/or any other suitable criteria (e.g., the passageof a predetermined amount of time from the closing of the switch 110).The process may continue in this manner as long as desired. In this way,the element 100 may pump heat from the thermal load 114 to the ambient112.

According to various embodiments, the control circuit 130 may utilizethe sensors 132, 134, 136, 138, 140 to control the various components ofthe element 100 to implement the process flow shown in FIGS. 3(a)-3(d).For example, the control circuit 130 may receive a signal indicatingthat the switch 108 is either open or about to open, indicating that thecurrent 302 should be stopped. The signal may, for example, originatefrom sensor 140, which may indicate a state of the switch 108. In someembodiments, the signal may be received from one or both of the sensors132, 134, which (e.g., collectively) may indicate a temperaturedifferential between the ambient 112 and the interface 106. The controlcircuit 130 may initiate the current 304 upon receiving a signalindicating that the switch 108 has closed or is about to close (e.g.,from one or more of sensors 140, 132, 134). Similarly, the controlcircuit 130 may receive information about the state of the switch 110and/or the temperature of the interface 106 and thermal load 114 viasensors 138, 132, and 136. This information may be used by the controlcircuit 110 to initiate and stop the current 304, as described above.

As described above, the control circuit 130 may, in some embodiments,also control the actuation of the heat switches 108, 110. For example,the control circuit 130 may sense the temperature(s) of the ambient 112,thermal load 114 and interface 106 (e.g., via sensors 134, 136 and 132).When the opening and/or closing thresholds of the heat switches 108,110, are reached, the control circuit 130 may cause the appropriateswitch 108, 110 to open or close, for example, as described above. Forexample, the switches 108, 110 may comprise components that may bebrought into physical contact, and therefore thermal contact, with oneanother on command of the control circuit 130 (e.g., through the use ofone or more stepper motors, solenoids, magnetic fields, etc.). Otherexample heat switches 108, 110 may comprise microelectronic machines(MEMS) and/or nano components actuated piezoelectrically and/orelectrostatically. In other embodiments, the switches 108, 110 maycomprise voids that may be alternately filled and emptied of aconductive gas, such as, for example, helium.

According to various embodiments, multiple thermoelectric elements maybe utilized in parallel. Figure s 5(a)-5(d) illustrates a process flowshowing the operation of one embodiment of a thermoelectric device 501comprising a plurality of thermoelectric elements 500 operating inparallel. The thermoelectric elements 500 may be elements, such aselements 100 of FIGS. 1 and 2, described above. For example, each of thethermoelectric elements 500 may comprise first and second components inelectrical contact with one another at an interface, paralleling thefirst and second components 102, 104 and interface 106 described above.The elements 500 may be connected in parallel. For example, theinterfaces of each of the elements 500 may be thermally connected to acommon ambient or thermal reservoir 502 via heat switches, parallelingthe heat switch 108 described herein. Further, the interfaces of theelements 500 may also be thermally connected to a common thermal load504 via heat switches paralleling the heat switch 110 described herein.A control circuit 506 may be constituted and operate similar to thecontrol circuit 130 described above. According to various embodiments,the control circuit 506 may control each of the thermoelectric elements500 collectively. Also, in some embodiments, the control circuit 506 maycomprise multiple portions that may or may not be in communication withone another, with each portion independently controlling one or more ofthe thermoelectric elements 500.

As illustrated in FIG. 5(a), the control circuit 506 may cause a current508 to flow across the interfaces of the elements 500 in a directiontending to cause the interfaces to cool (e.g., from p-type material ton-type material). In this way, each of the elements 500, as depicted inFIG. 5(a) may operate in a manner similar to the element 100 as depictedin FIG. 3(a). The interfaces of the elements 500 may heat, while theheat switches connecting the interfaces of the elements 500 to thecommon ambient 502 and the common thermal load 504 may be open,thermally isolating the elements from the ambient 502 and thermal load504. As the temperature of the interfaces of the elements 500 increases,the temperature differential between the interfaces of the elements 500and the common ambient 502 may increase to or above a closing thresholdof the heat switches separating the elements 500 from the common ambient502. This may cause these heat switches to close, resulting in a thermalconnection between the interfaces of the elements 500 and the commonambient 502. Alternatively, the control circuit 506 may close theswitches based on any suitable criteria. At or about the closing of theswitches between the elements 500 and the common ambient 502, thecontrol circuit 506 may cause the current 508 to cease. An exampleconfiguration of the elements 500 in this state is shown by FIG. 5(b).As shown in FIG. 5(b), each individual element may be configured, andmay operate, in a manner similar to that described above with respect toFIG. 3(b). For example, heat energy concentrated at the interfaces ofthe elements 500 may be conducted and/or dissipated to the commonambient 502.

As the temperature differential between the elements 500 and the commonambient 502 decreases, the switches separating the interfaces of theelements 500 from the common ambient 502 may open, causing substantialthermal isolation between the elements 500 and the common ambient 502.(E.g., the switches may open when the temperature differential betweenthe elements 500 and the common ambient 502 reaches and/or exceeds anopening threshold, or as determined by the control circuit 506.) At orabout the opening of the switches between the elements 500 and thecommon ambient, the control circuit 506 may cause a current 510 to flowthrough the elements 500 in a direction that causes cooling of therespective interfaces (e.g., from n-type material to p-type material).This configuration is illustrated in FIG. 5(c). The configuration andoperation of each individual thermoelectric element 500 shown in FIG.5(c) may be similar to the operation of the element 100, as illustratedin FIG. 3(c). For example, the interfaces of the elements 500 may coolas heat is driven away from the interfaces. As the elements 500 cool,the temperature differential between the interfaces of the elements 500and the common thermal load 504 may increase until reaching or exceedinga closing threshold of the heat switches between the interfaces of theelements 500 and the common thermal load 504. When the differentialreaches or exceeds the closing threshold of the heat switches betweenthe interfaces of the switches between the interfaces of the elements500 and the common thermal load 504. At or about the closing of theseswitches, the control circuit 506 may cause the current 510 to cease.

FIG. 5(d) shows the device 501 after the cessation of the current 510and after the switches between the interfaces of the elements 500 andthe common thermal load 504 have closed (e.g., in response totemperature differentials between the interfaces and common thermal load504 or by the control circuit 506). The configuration and operation ofeach individual thermoelectric element 500 shown in FIG. 5(d) may besimilar to the operation of the element 100, as illustrated in FIG.3(d). For example, heat from the common thermal load 504 may flow to theelements 500 until the temperature differential between the interfacesof the elements 500 is reduced to or below an opening threshold of therelevant switches, at which point the switches may close. At or aboutthe closing of the switches (e.g., the switches between the interfacesof the elements 500 and the common thermal load 504), the controlcircuit 506 may begin the current 508, putting the elements 500 in theconfiguration shown in FIG. 5(a). The process may continue as long asdesired and may have the effect of transferring heat from the commonthermal load 504 to the common ambient 502. The use of multiplethermoelectric elements 500 in the device may increase the capacity ofthe system compared to the use of only a single element 100 in thedevice 101.

FIGS. 6(a)-6(b) illustrate a process flow showing the operation of oneembodiment of a compound thermoelectric device 601. The compoundthermoelectric element may comprise one or more thermoelectric elements605, 603 connected to each other, to an ambient or thermal reservoir604, and to a thermal load 606 by heat switches 620, 622, 624. Element605 may comprise a first component 612 and a second component 614electrically connected by an interface 608. Similarly, element 603 maycomprise a first component 616 and a second component 618 electricallyconnected by an interface 610. The respective first components 612, 616,second components 614, 618 and interfaces 608, 610 of the elements 605,603 may be connected in a manner similar to that illustrated anddescribed above with respect to the thermoelectric element 100. Forexample, the first components 612, 616 and the second components 614,618 may be made from materials (e.g., p-type and n-type semiconductormaterial, respectively) that have different Seebeck coefficients suchthat current across the first components 612, 616 and second components614, 618 causes cooling at the interfaces 608, 610 in a first directionand heating at the interfaces 608, 610 in second direction. Also, theelectrical connections between the respective first components 612, 616and second components 614, 618 may not create rectifying pn junctions,as described herein above.

In a first state of operation, as illustrated by FIG. 6(a), the controlcircuit may cause a first current 650 to flow across the respectiveelements 605, 603 in the direction shown. For example, the current 650may flow across the element 605 from component 612 to component 614(e.g., from p-type to n-type). Accordingly, the element 605 (e.g., atthe interface 608) may heat. The current 650 may also flow across theelement 603 from component 618 to component 616 (e.g., from n-type top-type). This may cause the element 603 (e.g., at the interface 610) tocool. Although the current 650 is illustrated and described as a singlecurrent, it will be appreciated that current across the first element605 and current across the element 603 may be separate currents (e.g.,separately generated, separately switched, etc.).

Heat at the interface 608 may cause a temperature differential betweenthe interface 608 and the ambient 604 to exceeding a closing thresholdof the heat switch 620, causing it to close and allowing heat from theinterface 608 to be conducted from the element 605 and interface 608 tothe ambient 604. Similarly, a lack of heat (e.g., cool) at the interface610 may cause a temperature differential between the interface 610 andthe thermal load 606 exceeding a closing threshold of the heat switch624, causing it to close and allowing heat from the thermal load 606 tobe conducted to the element 603 (e.g., the interface 610). As shown inFIG. 6(a), the heat switch 622 may be open creating substantial thermalisolation between the elements 605, 603. Alternatively, the positions ofthe respective switches 620, 622, 624 may be controlled by the controlcircuit 602, according to any suitable method.

According to various embodiments, the heat switch 622 may be a one-wayheat switch. For example, in the configuration illustrated in FIG. 6(a),the interface 608 is heated while the interface 610 is cooled.Accordingly, there may be a significant temperature differential fromhot to cold between the interface 608, 610. The heat switch 622, invarious embodiments, may not close in response to a temperaturedifferential in this direction. For example, the heat switch 622 mayonly close in response to a temperature differential when the interface610 is hotter than the interface 608. In various embodiments, the otherheat switches 620, 624 may be similarly one-way. This may prevent theswitches 620, 624 from closing, and thus disrupting the operation of thethermoelectric device 601 due to extreme heat at the thermal load 606and/or extreme cold at the ambient 604.

Referring now to FIG. 6(b), the control circuit 602 may cause thecurrent 650 to cease and cause a current 652 to flow in a directionopposite to that of the current 650. This current may heat the interface610 of the element 603 and cool the interface of the element 605.Cooling of the interface 608 may cause the temperature differentialbetween the interface 608 and the ambient 604 to drop below an openingthreshold of the heat switch 620, causing the heat switch 620 to openand resulting in substantial thermal isolation between the element 605and the ambient 604. Similarly, heating of the interface 610 may causethe temperature differential between the interface 610 and the thermalload 606 to drop below an opening threshold of the heat switch 624,causing the heat switch 624 to open and resulting in substantial thermalisolation between the element 603 and the thermal load 606. At the sametime, heating of the interface 610 and cooling of the interface 608 maycause a temperature differential from the interface 608 to the interface610 to meet or exceed a closing threshold of the heat switch 622,causing it to close and create a thermally conductive path between theinterfaces 608, 610 and, thereby, between the elements 605, 603themselves. In this way, heat drawn to the interface 610 may beconducted to the interface 608. The thermoelectric element may operateas described, alternating between the configuration of FIG. 6(a) and theconfiguration of FIG. 6(b) for as long as desired. In effect, theoperation described may serve to pump heat from the thermal load 606 tothe ambient 604. Although the current 652 is illustrated and describedas a single current, it will be appreciated that current across thefirst element 605 and current across the element 603 may be separatecurrents (e.g., separately generated, separately switched, etc.). Asdescribed herein, the switches 620, 622, 624 may alternately be actuatedby the control circuit 602.

FIG. 7 illustrates a diagram of one embodiment of a-heat switch 700. Theheat switch 700 may be utilized as any of the switches 108, 110, 620,622, 624 described herein. As illustrated, the heat switch 700 comprisesa first terminal 702 mechanically and thermally coupled to a firstswitch element 706 and a second terminal mechanically coupled to asecond switch element 708. The first switch element 706 may be receivedwithin a cavity 710 of the second switch element 708. When the switch700 is in an open position, a gap 712 may exist between the firstelement 706 and the second element 708, preventing physical contactbetween the two. In some embodiments, the switch elements 706, 708 maybe maintained in a vacuum to prevent heat conduction across the gap 712by air.

The switch 700 may be opened and/or closed based on a temperaturedifferential between its terminals 702, 704. Mechanically, the switch700 may be closed by eliminating the gap 712 and bringing the elements706, 708 into physical contact with one another. This may occur, forexample, by some combination of thermal contraction of the element 708and/or thermal expansion of the element 706. This combination may bebrought about by a temperature differential between the terminals 702,704. For example, when the terminal 702, and thus the element 706, is ata higher temperature than the terminal 704, and thus the element 708,the element 706 may thermally expand relative to the element 708,narrowing the gap 712. This operation could alternately be viewed as theelement 708 thermally contracting relative to the element 706. Anycombination of thermal expansion by the element 706 and/or thermalcontraction by the element 708 may occur. The temperature differentialat which the gap 712 disappears and the elements 706, 708 enter thermalcontact with one another may be referred to as a closing thresholddifferential. According to various embodiments, the switch 700 may beconsidered a one-way heat switch. For example, a negative temperaturedifferential from the terminal 704 to the terminal 702 would not causethe switch to close. Heating the terminal 704 would cause the element708 to expand, thus tending to increase the gap 712. Cooling theterminal 702 would also tend to increase the gap 712 by thermallycontracting the element 706.

Once closed, the switch 700 may be re-opened according to any suitablemechanism. For example, reducing or reversing the temperaturedifferential between the terminals 702 and 704 may cause differentialexpansion of the elements 706, 708 sufficient to recreate the gap 712despite the fact that the elements 706, 708 are in thermal contact withone another when the switch 700 is closed. For example, while there is atemperature differential between the terminals 702, 704, there may be atemperature gradient between the terminals 702, 704, across the elements706, 708. Accordingly, the elements 706, 708 may not expand or contractuniformly (e.g., because one or both of the elements 706, 708 may nothave a single, uniform temperature). When the temperature differentialbetween the terminals 702, 704 reaches a value that causes a largeenough portion of the element 706 to thermally contract, and/or a largeenough portion of the element 708 to expand, contact between theelements 706, 708 may be broken. This may recreate the gap 712, causingsubstantial thermal isolation between the elements 706, 708 and theterminals 702, 704. The temperature differential which causes the switch700 to open may be referred to as the opening temperature differentialthreshold. The opening temperature differential threshold may, or maynot, be equal to the closing temperature differential threshold.

According to various embodiments, the elements 706, 708 may be made fromdifferent materials having different coefficients of thermal expansion.In this way, the closing and/or closing temperature differentialthreshold may be dependent on absolute temperatures of the terminals702, 704. FIG. 8 illustrates a diagram of another embodiment of a heatswitch 800 actuated by thermal differentials. The heat switch 800 mayoperate in a manner similar to that of the switch 700 and may havesimilar properties. A terminal 802 may be in thermal communication witha roughly cylindrical element 802 that may be received within a hollowelement 806, in thermal communication with a terminal 804. A gap 812between the elements 806, 808 may ensure substantial thermal isolation.Some combination of thermal expansion by the element 808 and/or thermalcontraction by the element 806 may eliminate the gap 812, bring theelements 806, 808 (and the terminals 802, 804) into thermal contact withone another. The switch 800 may have a closing temperature differentialthreshold and an opening temperature differential threshold, forexample, as described herein with respect to switch 700.

The examples presented herein are intended to illustrate potential andspecific implementations of the present invention. It can be appreciatedthat the examples are intended primarily for purposes of illustration ofthe invention for those skilled in the art. No particular aspect oraspects of the examples are necessarily intended to limit the scope ofthe present invention. For example, no particular aspect or aspects ofthe examples of system architectures, methods described herein arenecessarily intended to limit the scope of the invention.

It is to be understood that the figures and descriptions of the presentinvention have been simplified to illustrate elements that are relevantfor a clear understanding of the present invention, while eliminating,for purposes of clarity, other elements. Those of ordinary skill in theart will recognize, however, that these sorts of focused descriptionswould not facilitate a better understanding of the present invention,and therefore, a more detailed description of such elements is notprovided herein.

Moreover, the processes associated with the present example embodiments(e.g., process flows shown by FIGS. 3(a)-3(d), 5(a)-5(d) and 6(a)-6(b))may be executed by programmable equipment (e.g., control circuits 130,506, 602, etc.), such as computers. Software or other sets ofinstructions that may be employed to cause programmable equipment toexecute the processes. The processes may be stored in any storagedevice, such as; for example, a computer system (non-volatile) memory,an optical disk, magnetic tape, or magnetic disk. Furthermore, some ofthe processes may be programmed when the computer system is manufacturedor via a computer-readable memory medium.

It can also be appreciated that certain process aspects described hereinmay be performed using instructions stored on a computer-readable memorymedium or media that direct a computer or computer system (e.g., controlcircuits 130, 506, 602, etc.) to perform process steps. Acomputer-readable medium may include, for example, any non-transitorymedia such as, for example, memory devices such as diskettes, compactdiscs of both read-only and read/write varieties, optical disk drives,and hard disk drives. A computer-readable medium may also include memorystorage that may be physical, virtual, permanent, temporary,semi-permanent and/or semi-temporary. It will be appreciated that theterm non-transitory refers to the medium and not to any data storedthereon. For example, a random access memory (RAM) is non-transitory,although the data stored thereon may change regularly.

A “computer,” “machine,” “computer device,” “host,” “engine,” or“processor” may be, for example and without limitation, a processor,microcomputer, minicomputer, server, mainframe, laptop, personal dataassistant (PDA), wireless e-mail device, cellular phone, pager,processor, fax machine, scanner, or any other programmable deviceconfigured to transmit and/or receive data over a network. Computersystems and computer-based devices disclosed herein may include memoryfor storing certain software applications used in obtaining, processing,and communicating information. It can be appreciated that such memorymay be internal or external with respect to operation of the disclosedexample embodiments. The memory may also include any means for storingsoftware, including a hard disk, an optical disk, floppy disk, ROM (readonly memory), RAM (random access memory), PROM (programmable ROM),EEPROM (electrically erasable PROM) and/or other computer-readablememory media.

In various example embodiments of the present invention, a singlecomponent may be replaced by multiple components, and multiplecomponents may be replaced by a single component, to perform a givenfunction or functions. Except where such substitution would not beoperative to practice embodiments of the present invention, suchsubstitution is within the scope of the present invention. Any of theservers or computer systems described herein, for example, may bereplaced by a “server farm” or other grouping of networked servers(e.g., a group of server blades) that are located and configured forcooperative functions. It can be appreciated that a server farm mayserve to distribute workload between/among individual components of thefarm and may expedite computing processes by harnessing the collectiveand cooperative power of multiple servers. Such server farms may employload-balancing software that accomplishes tasks such as, for example,tracking demand for processing power from different machines,prioritizing and scheduling tasks based on network demand, and/orproviding backup contingency in the event of component failure orreduction in operability.

While various embodiments have been described herein, it should beapparent that various modifications, alterations, and adaptations tothose embodiments may occur to persons skilled in the art withattainment of at least some of the advantages. The disclosed embodimentsare therefore intended to include all such modifications, alterations,and adaptations without departing from the scope of the embodiments asset forth herein.

We claim:
 1. A thermoelectric device comprising: a thermoelectricelement comprising a first component and a second component with aninterface between the first component and the second component; a firstheat switch comprising a first terminal in thermal contact with theinterface and a second terminal in thermal contact with a thermalreservoir; a second heat switch comprising a first terminal in thermalcontact with the interface and a second terminal in thermal contact witha thermal load; and a control circuit configured to: with the first andsecond heat switches open, initiate a first current across thethermoelectric element from the first component to the second componentcausing the interface to heat; determine that a temperature differencebetween the interface and the thermal reservoir is greater than aclosing threshold for the first heat switch; close the first heat switchcreating a thermally conductive path between the interface and thethermal reservoir; stop the first current, wherein after the stopping ofthe first current, heat from the interface is transferred to the thermalreservoir; determine that the temperature difference between theinterface and the thermal reservoir is less than the closing thresholdfor the first heat switch; open the first heat switch; initiate a secondcurrent across the thermoelectric element from the second component tothe first component causing the interface to cool; determine that atemperature difference between the interface and the thermal load isgreater than a closing threshold for the second heat switch; and closethe second heat switch creating a thermally conductive path between theinterface and the thermal load.
 2. The thermoelectric device of claim 1,wherein the control circuit is further configured to: stop the secondcurrent, wherein after the stopping of the second current, heat from thethermal load is transferred to the interface; determine that thetemperature difference between the interface and the thermal load isless than the closing threshold for the second heat switch; and open thesecond heat switch.
 3. The thermoelectric device of claim 2, wherein thefirst component comprises a p-type semiconductor and the secondcomponent comprises an n-type semiconductor.
 4. The thermoelectricdevice of claim 2, wherein the thermal reservoir is an ambientenvironment of the thermoelectric element.
 5. The thermoelectric deviceof claim 2, wherein the thermal load is a device generating waste heat.6. The thermoelectric device of claim 2, wherein the first component andthe second component are not in physical contact with one another. 7.The thermoelectric device of claim 6, wherein the interface comprises anelectrically conductive component physically separating the firstcomponent and the second component.
 8. The thermoelectric device ofclaim 1, further comprising: a second thermoelectric element comprisinga first component and a second component with an interface between thefirst component and the second component; a third heat switch comprisinga first terminal in thermal contact with the interface of the secondthermoelectric element and a second terminal in thermal contact with thethermal reservoir; a fourth heat switch comprising a first terminal inthermal contact with the interface of the second thermoelectric elementand a second terminal in thermal contact with the thermal load; andwherein the control circuit is further configured to: initiate a thirdcurrent to flow across the second thermoelectric element from the firstcomponent to the second component causing the interface of the secondthermoelectric element to heat; determine that a temperature differencebetween the interface of the second thermoelectric element and thethermal reservoir is greater than a closing threshold for the third heatswitch; and close the third heat switch causing a thermally conductivepath between the interface of the second thermoelectric element and thethermal reservoir.
 9. The thermoelectric device of claim 8, wherein thecontrol circuit is further configured to: stop the third current,wherein after the stopping of the third current, heat from the interfaceof the second thermoelectric device is transferred to the thermalreservoir; determine that the temperature difference between theinterface of the second thermoelectric element and the thermal reservoiris less than the closing threshold for the third heat switch; open thethird heat switch; initiate a fourth current across the secondthermoelectric element from the second component to the first componentcausing the interface of the second thermoelectric element to cool;determine that a temperature difference between the interface of thesecond thermoelectric element and the thermal load is greater than aclosing threshold for the fourth heat switch; close the fourth heatswitch creating a thermally conductive path between the interface andthe thermal load; stop the fourth current, wherein after stopping thefourth current, heat from the thermal load is transferred to theinterface of the second thermoelectric element; determine that thetemperature difference between the interface of the secondthermoelectric element and the thermal load is less than the closingthreshold for the fourth heat switch; and open the fourth heat switch.10. The thermoelectric device of claim 9, wherein the first and thirdcurrents are concurrent, and wherein the second and fourth currents areconcurrent.
 11. The thermoelectric device of claim 1, further comprisinga temperature sensor positioned to sense a temperature of the interface;a temperature sensor positioned to sense a temperature of the thermalreservoir; and a temperature sensor positioned to sense a temperature ofthe thermal load.
 12. A thermoelectric device comprising: a firstthermoelectric element comprising a first component and a secondcomponent with an interface between the first component and the secondcomponent; a second thermoelectric element comprising a first componentand a second component with an interface between the first component andthe second component; a first heat switch comprising a first terminal inthermal contact with the interface of the first thermoelectric elementand a second terminal in thermal contact with a thermal reservoir; asecond heat switch comprising a first terminal in thermal contact withthe interface of the first thermoelectric element and a second terminalin thermal contact with the interface of the second thermoelectricdevice; a third heat switch comprising a first terminal in thermalcontact with the interface of the second thermoelectric device and asecond terminal in thermal contact with a thermal load; and a controlcircuit configured to: open the second heat switch; initiate a firstcurrent directed across the first thermoelectric element from the firstcomponent to the second component to cause heating at the interface ofthe first thermoelectric element; initiate a second current directedacross the second thermoelectric element from the first component to thesecond component to cause cooling at the interface of the secondthermoelectric element; closing the first heat switch to create athermally conductive path between the first thermoelectric element andthe thermal reservoir, wherein heat from the first thermodynamic elementis transferred to the thermal reservoir while the first heat switch isclosed; closing the third heat switch to create a thermally conductivepath between the second thermoelectric element and the thermal load,wherein heat from the thermal load is transferred to the secondthermoelectric element while the third heat switch is closed; stop thefirst and second currents; initiate a third current directed across thefirst thermoelectric element from the second component to the firstcomponent to cause cooling at the interface of the first thermoelectricelement; initiate a fourth current directed across the secondthermoelectric element from the second component to the first componentto cause heating at the interface of the second thermoelectric element;open the first heat switch; open the third heat switch; and close thesecond heat switch.
 13. The thermoelectric device of claim 12, whereinthe first component of the first thermoelectric element comprises ap-type semiconductor and the second component of the firstthermoelectric element comprises an n-type semiconductor.
 14. Thethermoelectric device of claim 12, wherein the thermal reservoir is anambient environment of the first and second thermoelectric elements. 15.The thermoelectric device of claim 12, wherein the thermal load is adevice generating waste heat.
 16. The thermoelectric device of claim 12,wherein the first component and the second component of the firstthermoelectric element are not in physical contact with one another. 17.The thermoelectric device of claim 16, wherein the interface of thefirst thermoelectric component comprises an electrically conductivecomponent physically separating the first component and the secondcomponent.
 18. The thermoelectric device of claim 12, wherein the firstcomponents of the first and second thermoelectric elements and thesecond components of the first and second thermoelectric elements are inelectrical contact with each other such that the first and secondcurrents are a common current and the third and fourth currents are acommon current.
 19. The thermoelectric device of claim 12, wherein thecontrol circuit is further configured to open the first heat switch whena temperature differential between the interface and the thermalreservoir drops below a thermal switching threshold of the first heatswitch.
 20. The thermoelectric device of claim 12, wherein the controlcircuit is further configured to open the third heat switch when atemperature differential between the second interface and the thermalload drops below a thermal switching threshold of the third heat switch.21. The thermoelectric device of claim 12, wherein, while the secondheat switch is closed, heat from the second interface is dissipated, viathe second heat switch, to the first interface and wherein the controlcircuit is further configured to open the second heat switch when atemperature differential between the second interface and the firstinterface drops below a thermal switching threshold of the second heatswitch.